FIG. 1 of the accompanying drawings schematically illustrates a conventional butterfly valve arrangement 10 in which a butterfly plate 12 positioned in a duct 14 is rotated about an axis defined by a spindle or shaft 16 in order to vary the rate at which fluid flows through the duct. Typically, the plate 12 is rotated via torque applied by an external actuator 18 through the shaft 16.
A series of arrows 20 generally illustrates the static pressure profile resulting from the aerodynamic or hydrodynamic forces acting on the butterfly plate 12. The overall effect of the static pressure may be represented by a center of pressure (indicated by the arrow 22) which tends to force the plate 12 to the closed position. This force must be countered or overcome by energy supplied to the actuator 18 in order to retain the position of the plate 12 or further open the valve 10.
As a general matter, in order to lower the externally-supplied energy required to match or exceed the hydrodynamic forces acting on the plate 12, the center of pressure 22 should be favorably altered in relation to the axis of rotation That is, either the center of pressure 22 should be aligned with or moved closer to the shaft 16, or the shaft should be aligned with or moved closer to the center of pressure.
The above-referenced application teaches, among other things, that if in the design of a butterfly valve one provides for relative translational movement between the shaft 16 and the plate 12, then the bulk of the energy required to torque the plate can be provided by the aerodynamic forces acting thereon. The present invention employs this and other teaching contained in said application to provide a butterfly-type check valve.